You can perform the pocket maneuver when you are in a classroom or at work. Say you are sitting in your chair, and you feel a boner coming, pull the pocket of your pants out and feed your cock through the pocket. This will kind of hide your erection but it does feel very nice. This technique works the best if you are wearing boxers and athletic shorts/pants.

Your Friend - "Crap, I'm starting to get a massive boner."
You - "Oh no problem, just pull The Pocket Maneuver and it will hide it AND it feels cool. I'm using that technique right now."